Victron - installation / upgrade

Inverters Victron
41

Can I ask some silly questions:
I’m trying to understand the appeal/motivation behind adding a Fronius to a system.
Context: I have 3x MPIIs on a grid-tied system, for a total generation capacity of 7.2kW (21x410W panels & 4xPylon batteries as well, not that I think that’s relevant here?)

What would the motivation be behind adding a Fronius to this system? Or have I missed something fundamental? I ask because I don’t feel like I’ve hit a “limit” with my system, so trying to work out what the extra component would add.

42

AC PV inverters is much more efficient than DC PV, so if you use lots of electricity during the day when the sun is shining and especially also if you feed back, then using a Fronius for that will be much more efficient than a Victron MPPT plus inverter.

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43

So I assume you have maybe 3 MPPTs at the moment, charging your batteries?

It is possible to get a Fronius (or other brand) instead of an MPPT. So you connect some panels on the Fronius. This is a PV inverter, not an MPPT. During the day, when the sun is shining, this would increase the amount of load you can run off your PV. Say you have 3x5kW MPIIs, then you have 15kW of loads you can meet. If you, instead of an MPPT, get a 5kW Fronius, for example, then you would be able to meeting 20kW of loads.

A second order benefit is that the PV inverter is more efficient if you use the power immediately. Losses on the MPPT side might be roughly 20% while it might be only 10% on the PV inverter side (only if you use the power immediately).

If you do not use the power immediately, and you want to charge your batteries from the PV inverter, then you would have a full cycle loss of roughly 30% (so worse than the MPPT solution).

To me, the main benefit is to be able to invert more during the day, while the sun is shining, to run non-essentials. Because it isn’t a “backup” inverter, you don’t need to buy more batteries. As long as your MPIIs have sufficient battery capacity (and inverting capacity) for your back-up loads, your system should be stable.

All the above is how I understand it, I don’t myself have a PV inverter. Looking at getting one though, when a bit of roof space opens up again.

I wouldn’t say “much” more. It is about 10%. But also, PV is DC in nature, so technically isn’t it just a high voltage DC → AC inverter compared to your Multi which inverts from a low voltage DC to a high voltage AC?

44

I have 2 MPPTs (one per panel direction, 15 panels on one bigger MPPT, 6 panels on a smaller one)
One MPII is a GX, so that does the brain work, the other 2 are pure inverters.

45

I don’t think it makes sense to change anything if you have enough inverting capacity. For me, I do want to buy more panels, so I need to decide between a PV inverter (that can communicate with my GX) or another MPPT for them. I’m looking at a PV inverter to give me that extra capacity to run more appliances in the scullery at the same time (scullery isn’t on my backup, at least not automatically) without having to buy from the grid.

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46

Thanks. Not looking to change anything, as stated I’m very happy.
Just interested in furthering my understanding :slight_smile:

47

I was where you are, sometimes I’m still as confused as before I started.

Fronius or Solis, Victron or Sturder, FreedomWon or Pylontech. MPPT or not … you don’t know what you don’t know.

I have deduced, over the years, that some will focus on the highest efficiency system. The next person does not care about that, more interested in other core functionalities, some focus on expansion potential … and/or whatever else makes us tick as individuals.

You can also use a trusted installer having loads of experience, who installs you the best system they can … on what YOU told them you wanted, YOU thought you wanted, YOU could afford at the time.

You don’t know what you don’t know.

Like, having installed your preferred system with Xkw of panels, the weather comes past and says nope, you can get a couple of 100watts only … for days on end!

Or you missed that palm tree/chimney, leaves in the neighbor’s property, affecting your panel production sometime/s during the year.

Or the batteries are too small, lifestyle changes are needed, even more automation is needed … rabbit hole man, rabbit hole.

Or you need a bigger inverter = more batteries required + more panels = even more expenses, and don’t have the roofspace or what not.

With all that, all the carefully deliberated engineering specs are out the door man! Gone. The system is not exactly what you thought, too small, too big, not what you thought you wanted or needed.

So, over time, having done all I can to make mistakes, to mitigate those bummers having lived them all, done them all, my advice: Start smaller.

Why?

After you have bought your system, having used it for a min of 1 year (summer and winter), having adjusted the lifestyle of the house as best you can to fit the system, I promise you, you will change your mind, you will want to alter this or that or whatever you can.

Walking the talk versus Talking the walk with your own system, having deduced with actual facts and figures, what it is you really need/want, what works for YOU.

Start smaller and enjoy the journey. Buy, sell, upgrade. Have some fun.

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48

Jykenmynie posted on my setup as above. Apart from that, for some background you can have a look at this Design guide where I cover all the background info It may be helpful.

Groetnis

49

It’s a bit more.

The MPPT is around 95% efficient. Then it goes onto the DC bus, from where it is used directly (so we can ignore the battery efficiency), but an LF design inverter like the Multi is between 85% and 93% efficient (in my experience, around 88% at 80%), giving an overall efficiency of 83%. The Fronius MPPT is 95% efficient. So it’s more like 12% more efficient to AC-couple the PV.

But charging batteries from the AC side is similarly inefficient, as the Multi charges at around 90% or so, around 10% more efficient to charge with a DC-coupled MPPT.

So the way to decide, is to look at when you use the majority of the energy. If you use more than two thirds during the day, AC-couple it. If you store more than two thirds for later use, DC-couple it.

But a PV-inverter does cost a bit more. And in an off-grid system, you must DC-couple at least some of the PV, otherwise the system can deadlock when the battery goes dead.

That is another reason why more modern design HF inverters may be a better option. These inverters don’t buck the PV down to battery voltage. Instead they boost it directly to grid-voltage (like a PV-inverter), but they run a buck/boost stage down to battery. Victron’s new Multi-RS is in this category (as is Goodwe, Sunsynk, etc).

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50

Jip, I think I’ve noted before that to me the rule of thumb would be to size the MPPTs for your nighttime consumption and the PV-inverter for daytime consumption. Something like that. If you need to choose one, well you need to take the one that makes most sense for your usage patterns.

And obviously a high voltage DC battery system just adds to the efficiency advantages? Like that new Fronius hybrid inverter. I think it takes a HV battery pack. I’ve not done much reading on it, but it would be interesting to see whether it integrates well with say a Fronius PV-inverter if you want to expand.

However, doesn’t the capacitance of an LF design give a bit more stability to a system that would be running off-grid quite a bit of the time - like dealing with surges etc. of compressors/pumps going on? It is rare that a well developed older design has only disadvantages, but no advantages over a newer design…

51

Somewhat off-topic, but I still like the idea of a small amount of AC microinverters to just supply the “no-one home” base load of the house. So for the most part the inverter is idle as AC is taken care of and DC is charging batteries. Being just a small amount of watts for base load also meant that you can use some smaller panel/s to fit on odd sides of the roof you were not using anyway.

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52

Yes! I will say this, my blood may be blue, but man… the Fronius Hybrid is one really nice machine. A little costly, but really nice.

In the end, these things tend to evolve in any case. For myself, I moved house, and my load patterns changed. For optimum efficiency I really should move two thirds of my PV to a PV-inverter.

Or… I can ignore the 12% energy tax and run what I’ve got.

The other big upside to AC-coupling, which I have to mention: Makes it much simply if the PV is far away from the batteries. You already have an AC-reticulation system. Might as well use it!

Back to the topic at hand, this guy has a big battery bank and is heading towards what is essentially an off-grid system. The Quattro he is looking at is the right compromise. In my opinion anyway.

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53

Also getting back to the topic at hand, the OP said somewhere he only recently bought the Narada batteries, so they are basically brand new.

I would serously consider flipping those batteries and getting something else which properly communicates with Victron. Maybe lose a few bucks now, but in the long run and especially if the intention is to end up with a 60 kWh battery bank, I think proper communication with the Victron system will be a game changer.

54

As much as I hate this - you right. The question is who provides single 10kw batteries as I don’t want to go do a million smaller batteries :slight_smile: example I see Pylontech (which seems to have good support and availablity in ZA) max is 4.8KW per battery.

55

Jitte! I just had a quick look to see what HV battery packs go for… I think I am more than happy to live with my 48V system, thank you very much. Perhaps the website I looked at isn’t the cheapest, and the BYDs I found isn’t the cheapest, but joh ~R150k for 12.8kWh. I can get a lot of inefficiencies with the kWhs of 48V batteries I can buy for R150k.

Why would HV banks be so much more expensive? The protection equipment/BMS? Is the balancing of the cells much more difficult because one flat cell invalidates the bank?

Isn’t it better having many smaller batteries (ignoring the cabling) because if one goes, you replace that one.

56

Look at Freedom Won, they are highly recommended, they build 5, 10, 15, 20 kWh and even bigger packs.

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57

It is better to have more than one module, in my opinion anyway, so that trouble in any particular module (causing it to disconnect from the DC bus) does not take down the whole house. So for the typical guy aiming for around 12kWh or so, 4 x 3kWh Python module is a good setup. But I concur that 20 modules (to get up to 60kWh) might be a bit much. That’s almost two 48U racks full, and you will need an LV-hub. Then again, once you have it assembled, that makes up a very neat little setup.

The 4.8kWh options, as far as I know, have slightly different specs, either a lower DoD or a shorter cycle life or something. I just remember there was something that made the US3000 the better option.

But as @JN.V said, FreedomWON. They make that size battery.

@jykenmynie , also check the BlueNova batteries, they have HV options as well.

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58

my 2 shillings

sometimes teach a man to fish and sometimes point him to a michelin star restaurant that does a mean deconstructed fish and chips.

I suspect you are not 100% certain exactly what you want to achieve and also are looking at a potentially very big system. Learning and DIY’ing is all well and good but the current/voltages at play could lead to injury/death (could be basic typos but I notice what looks like uncertainty around kW vs kWh for instance). When you start paralleling batteries maximum discharge rate etc. are not always as simple as (n)X(batteries). Also looks like you have more than once made purchases of components not best suited to what you want/need and possibly not entirely compatible with one another. i.e. I suggest get a decent system designer involved - but don’t stop learning. :slightly_smiling_face:

If you want to tinker and code and automate Victron looks like one of the better options form my perspective. If you just want data availability there are a couple of options not yet mentioned (like MLT) but most of the brands offer some version of it. If you want “the best”… does not exist (unless a very specific list of criteria can be defined).

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59

One more thing to add about Narada batteries. I assume they are Lithium units with a CAN-bus port. Many battery makers are quite good at copying the de-facto CAN-bus standard from somewhere, so the odds are that it might even be detected as a generic CAN-bms battery. In which case… you’re done.

Then again, some copy the “Pylontech” protocol down to the identifying marks, causing it to be incorrectly detected as a Pylontech battery, and then treated as a 15-cell battery. To the great consternation of people who were first happy to see that “it works” and then dismayed to see that it doesn’t.

(Note to chinese battery makers… don’t copy the protocol as is… remove the PN from 0x359!).

60

might be time to step away from the coding for a bit… :wink:

/end derail

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